It is not hard to make Pine read and send GPG-encrypted or -signed messages. Several tools are available that glue gpg and pine together, and I use Pine Privacy Guard (PPG). This is a small Perl script that does all the hard work.

You can edit ~/.pinerc directly (look for the customized-hdrs= line) or configure from within pine (Setup > Config > Whereis > customized-hdrs)
Of course, the example GPG fingerprint and key-URL are mine, and you should substitute your own.